Research On High-Q FBAR And Its Filter Design

The development of fifth-generation mobile communication（5G）technology has driven the rapid development of industries such as mobile communication,autonomous driving and telemedi-cine.RF modules are important in communication devices,and filters are indispensable devices in RF modules.Compared with other types of filters,FBAR（Film Bulk Acoustic Resonator）filters are small in size,high in operating frequency and high in power capacity,and are the mainstream RF module in 4G and 5G communication devices.In this paper,we will focus on FBAR resonators and filters based on aluminum nitride（Al N）and scandium-doped aluminum nitride（Al Sc N）,analyze the effects of electrodes and piezoelectric materials on the bulk acoustic wave devices,and then discuss the losses in FBAR-type devices,propose improvement solutions,and finally design and prepare FBAR filters.The details of the study are as follows.（1）Firstly,the working principle of FBAR and the Lamb wave propagation characteristics in piezoelectric materials are analyzed.Combining the two equivalent circuit models of FBAR resona-tors,MBVD and Mason model,an improved Mason model is derived and the equivalent circuit sim-ulation is established in ADS for verification.（2）The effects of different piezoelectric materials and electrode structures on FBAR are com-pared.The acoustic wave loss in the FBAR is discussed and the acoustic wave dispersion phenome-non of the resonator is analyzed,and a double bump optimization structure based on Lamb waves is proposed to enhance the Q value of the FBAR.Subsequently,based on the loss mechanism of FBAR resonators,a piezoelectric-solid heat transfer multi-physics field coupled thermal simulation model is established to analyze the thermal characteristics of FBAR resonators.（3）The effects of capacitance and inductance on FBAR were analyzed,and FBAR filters with a stepped topology were designed using a modified Mason model simulation.A full-wave acoustic-electromagnetic simulation model was established to analyze the effect of layout of the layout on the FBAR filter.The temperature distribution of the filter operating at different frequencies was then analyzed to verify the design of the high-power filter.（4）Finally,the filters of different piezoelectric materials are designed and prepared by MEMS processing,and the piezoelectric properties of different materials are analyzed by real measurement comparison.The final prepared resonator has a series resonator frequency of 3419 MHz and a Q value of 1080.the filter bandwidth based on_0.80.2piezoelectric material is 240 MHz and the inser-tion loss is-2dB.